1. Field of the Invention
This invention relates to gravity gradiometer systems and more specifically to a gravity gradiometer compass.
2. Description of the Prior Art
A gravity gradiometer system delivers six outputs, representing the six elements of the local gravity gradient tensor. With reference to a local coordinate system whose axes are directed northward, eastward and downward, the six outputs may be labelled .GAMMA..sub.NN, .GAMMA..sub.EE, .GAMMA..sub.DD, .GAMMA..sub.NE, .GAMMA..sub.ND, .GAMMA..sub.ED.
Currently in the United States, there are three approaches to developing gravity gradiometer instruments. one approach is generally described in U.S. Pat. No. 3,731,537, issued May 8, 1973 to Trageser, and a second approach is generally described in U.S. Pat. No. 3,722,284, issued May 27, 1973 to Weber et al, assigned to Hughes Aircraft Company. The third approach is described in a paper prepared by E. H. Metzger for the AIAA Guidance and Control Specialist Conference, Hollywood, Fla. Aug. 8-9, 1977, and entitled "Recent Gravity Gradiometer Developments".
Any of these gravity gradiometer instruments may be attached to a gyroscopically stabilized level platform to provide a gravity gradiometer system suitable for use on a ship or other vehicle.
Moving vehicles such as ships typically include gyrocompasses to determine the heading of the ship. The inclusion of a gyroscopically stabilized gravity gradiometer on board a ship would result in a duplication of gyroscopic components common to both the gravity gradiometer system and the gyrocompass. Accordingly, modifying the gravity gradiometer to perform the additional function of a gyrocompass would result in a significant cost saving and would provide a highly accurate gyrocompass.